A new breed of mass transit facilities has been created to help alleviate the growing world-wide transportation problem which manifests itself in choked highways, saturated air lanes and financially floundering railroads. Particular attention has been directed to tracked air cushion vehicles (TACVs), which are similar to the Hovercraft air cushion vehicles in commercial service across the English Channel, and magnetic levitation vehicles (MAGLEVs), which are train-like vehicles suspended over a track by magnetism and propelled by a linear induction motor.
The TACV is essentially a combined passenger and power unit that is lifted off its guideways by powerful, downward thrusting fans which create an air cushion to virtually eliminate friction. Such units can be propelled forward by one of several means over a suitable track or guideway. A preferred means of propelling TACVs is the virtually noiseless and nonpolluting linear induction motor (LIM) such as that recently successfully tested by the British at Erith. Other propelling methods have involved the use of noisy propellers. A TACV operated in France near Orleans straddles a center rail as its guideway and uses a turbine-driven propeller to supply forward thrust.
Demonstrations in Germany established the feasibility and many of the advantages of MAGLEVs. At the German demonstrations a five-ton car was suspended by electromagnets and propelled by a LIM at speeds up to 40 miles per hour over an L-shaped experimental track. The apparatus used to magnetically suspend and propel the car is illustrated in FIG. 1. Basically, car 10 is suspended by powerful electromagnets 12 and 13 which face upward and pull against the underside of L-shaped rails 14 and 15. The rails are mounted on U-shaped brackets 16 and 17, respectively, to form the track or guideway. When electromagnets 12 and 13 are de-energized car 10 sets down against the top of the rails on skid blocks 19 and 20. A separate set of magnets 22 and 23 face the vertical surface of rails 14 and 15 to provide necessary lateral guidance. Car 10 is propelled by LIM 25 which reacts against a stationary aluminum plate (rotor) 28 to drive the car forward. LIM 25 is also used to apply necessary braking force to car 10.
Electromagnets 12 and 13 for the MAGLEV illustrated by FIG. 1 must be continuously activated in order to maintain suspended car 10 in the desired position. Very large steady state currents are required by the electromagnets in order to effect the necessary control. Because of the steady state current requirements, various inherent problems such as thermal problems, size and weight problems and power supply problems must be considered when attempting to obtain a practical self-contained suspension system which can be used in connection with a MAGLEV.
Alternate means, which has been proposed for magnetically suspending a vehicle but perhaps not constructed, is illustrated in FIG. 2 in which superconducting magnets 30 and 31 are suggested for suspending MAGLEV 33 over aluminum roadway 35 and 36 by eddy current repulsion. According to this proposed system the magnetic field is provided by magnets 30 and 31 which are cooled by cryogenic material, such as liquid helium 37 and 38, stored on board. In addition to the stored helium, gaseous helium would have to be refrigerated to a liquid by an onboard refrigeration system. It is intended that as long as the refrigeration is maintained the magnets should support the MAGLEV. Wheels, not shown, are proposed to be provided for travel at speeds 35-40 miles per hour and/or in case the refrigeration system should fail. A LIM with stator 39 is proposed for propelling MAGLEV 33.
Since there is no physical contact between a MAGLEV and the roadway, other than collector shoes which wipe against one or more rails, the power rail(s) and collector shoes are the only parts which are subject to wear and which can cause noise. The absence of mechanical loading means that a minimum of track maintenance is required. Another distinct advantage of the MAGLEV is its safety. The magnetic suspension system can be designed, as in FIG. 1, to lie beneath the track to help prevent derailment in the event of a crash.
MAGLEVs require less power and are generally quieter than TACVs. Although electromagnetic suspension systems require only about one-seventh the power needed by Hovercraft type vehicles, electromagnetic suspension systems still require a great amount of electric power for magnetic support. Accordingly, one of the principal problems with electromagnetic suspension systems designed for MAGLEVs has been the need for devising a way of continually supplying the correct amount of electromagnetic force to keep the system properly positioned. The required electromagnetic force varies with changes in vehicle load, speed, centrifugal force built up on curves, and the like. Cryogenic magnet systems proposed for suspending MAGLEVs offer theoretical direct electrical power advantages but entail disadvantages in other respects. The cryogenic systems for such vehicles require large amounts of power to operate the cooling system which must maintain the liquid helium at a temperature of about 4.degree.K.
The revolutionary development of a magnetic suspension system requiring virtually zero power, as set forth in copending Lyman application Ser. No. 317,047, filed Dec. 20, 1972 now U.S. Pat. No. 3,860,300, has made it possible to develop a virtually zero power linear magnetic bearing which can be used to support MAGLEVs.